1. The Field of the Invention
This application relates generally to drill bits and methods of making and using such drill bits. In particular, this application relates to core drill bits with an extended crown height and methods of making and using such drill bits.
2. Discussion of the Relevant Art
Often, core drilling processes are used to retrieve a sample of a desired material. The core drilling process connects multiple lengths of drilling rod together to form a drill string that can extend for miles. The drill bit is located at the very tip of the drill string and is used to perform the actual cutting operation. As a core drill bit cuts its way through the desired material, cylindrical samples are allowed to pass through the hollow center of the drill bit, through the drill string, and then can be collected at the opposite end of the drill string.
Many types of core drill bits are currently used, including diamond-impregnated core drill bits. This drill bit is generally formed of steel or a matrix containing a powdered metal or a hard particulate material, such as tungsten carbide. This material is then infiltrated with a binder, such as a copper alloy. As shown in FIG. 1, the cutting portion 202 of the drill bit 200 (the crown) is impregnated with synthetic diamonds, natural diamonds, or super-abrasive materials (e.g., polycrystalline diamond). As the drill bit grinds and cuts through various materials, the cutting portion 202 of the drill bit 200 erodes, exposing new layers of the sharp natural or synthetic diamond, or other super abrasive materials.
The drill bit may continue to cut efficiently until the cutting portion of the drill bit is totally consumed. At that point, the drill bit becomes dull and must be replaced with a new drill bit. This replacement begins by removing (or tripping out) the entire drill string out of the hole that has been drilled (the borehole). Each section of the drill rod must be sequentially removed from the borehole. Once the drill bit is replaced, the entire drill string must be assembled section by section and then tripped backs into the borehole. Depending on the depth of the hole and the characteristics of the materials being drilled, this process may need to be repeated multiple times for a single borehole. As a result, drill bits that last longer need to be replaced less often.
The crown heights for these drill bits are often limited by several factors, including the need to include fluid/debris ways 206 in the crown shown in FIG. 1. These fluid/debris ways serve several functions. First, they allow for debris produced by the action of the bit to be removed. Second, they allow drilling muds or fluids to be used to lubricate and cool the drill bit. Third, they help maintain hydrostatic equilibrium around the drill bit, preventing fluids and gases from the material being drilled from entering the borehole and causing blowout.
These fluid/debris ways are placed in the tip of the cutting portion of the core drill bit. Because the cutting portion of the core drill bit rotates under pressure, it can lose structural integrity because of the gaps 208 in the crown and then become susceptible to vibration, cracking, and fragmentation. To avoid these problems, the crown height of diamond-impregnated core drill bits is typically limited to heights of 16 to 17 millimeters or less. But with these shorter heights, though, the drill bits need to be replaced often because they wear down quickly.